This application describes four projects designed to explore the pathogenesis of electrophysiologic abnormalities produced by myocardial ischemia and/or myocardial infarction. First, the equivalent generator properties of lesions produced by coronary ligation in isolated, perfused rabbit and dog hearts will be quantitated. Dipolar and nondipolar features will be studied to determine the value of such measurements in sizing acute myocardial infarction. Second, total thoracic body surface isopotential maps will be constructed from patients with acute myocardial infarction. These maps will be examined to assess generator properties and to determine if such maps offer significant advantage over standard ECG and left precordial electrode systems. Third, isopotentials maps will be drawn during supine, submaximal exercise stress tests from normals and from patients with coronary disease to explore the pathogenesis of junctional and ST depression and to evaluate the diagnostic value of various precordial lead systems. Last, electrical transmission through hypoxic and ischemic lesions will be studied in vitro using microelectrode techniques and in vivo using transmural plunge electrodes.